Scientists Say Cryosleep Is the Only Way for Humans to Achieve Interstellar Travel

Bad news, Star Wars/Trek/Gate fans. Scientists have come out and said that faster-than-light travel, while a fun trope of science fiction, is flat-out impossible for humans to achieve in real life. But before you get too disappointed that we'll never get to travel to other galaxies with a warp drive, we might still be able to visit faraway space locations, as long as we sleep all the way there, Ellen Ripley-style.

FTL travel is an all-too-common device in sci-fi, but in real life, it's just plain impossible. Until we disprove the general theory of relativity, which is not at all likely, it goes against everything we know about the laws of physics.

"We cannot even come up with a physically consistent theory for how faster than light travel would work, much less conceive of engineering such a thing," hard sci-fi author Karl Schroeder told io9. "FTL is, in our universe as we understand it today, a complete fantasy rather than merely an 'as-yet undeveloped technology.'"

Some sci-fi movies and books get around this little problem by depicting their astronauts traveling through wormholes, most recently Christopher Nolan's Interstellar, this is also considered to be effectively impossible for humans to achieve. Wormholes are essentially just shortcuts in spacetime, so theoretically we should be able to use them to jump to interstellar space, but the energies required to keep them open for a spaceship to pass through are unimaginably high.

So there is no version of faster-than-light travel that is realistic; however, we might still be able to visit exoplanets if we can figure out cryosleep. While safely hibernating for a period of time that would allow a human to travel outside of our solar system is not within our reach now, it is at least conceivable based on the progression of current technologies.

"Based on what we now know, FTL is either impossible, or would require energies that are flat out ridiculous. Storing brains for a long period of time is merely very, very hard," said Terry Johnson, a biology professor at UC Berkeley.

Hibernation—or "hypersleep," as it's called in the Alien movies—is the best path to interstellar travel because although it's not possible now, it's based in known biological principles. Scientists just discovered, for example, that cryogenically frozen tardigrades, or "water bears," could be revived after 30 years of hibernation.

"There are many different paths to long-term hibernation," said Schroeder. "We already know that living things can be revived unharmed after very long periods."

And although it's much more complicated to extend principles of animal hibernation to humans, since we're significantly more complex and fragile than tardigrades, NASA is already working on a solution. They are currently conducting research on extended sleep, or "torpor," in the effort to send a manned mission to Mars. And there are many other research projects that are looking into a cooling stasis for humans, particularly for medical procedures.

"Right now, we are working to cool people for one to three days," said Kelly Drew, a professor at the Institute of Arctic Biology at the University of Alaska, Fairbanks. "If we get this figured out, the next step will be to cool them for several days, maybe a month. We have a long ways to go to make it a hundred, or a thousand, years."

While we technically have the ability to freeze human bodies already, the trick is figuring out how to cool the body without significant damage. When mammalian cells are frozen, ice crystals form inside them, causing weakened cell membranes and sometimes punctures. So brain damage, in particular, is extremely difficult to avoid when attempting to freeze a human for a long period of time.

"If you freeze a person for 100,000 years, there's likely going to be a lot of damage done," said Johnson. "Chemistry is slow at low temperatures, but it doesn't stop entirely, and you're giving it plenty of time to wreak havoc. Entropy marches on. [It might march slowly,] but 100,000 years is a long march."

There are several different ways we might get around these pesky practical issues, such as genetically engineering humans to have cell walls, like plants have, or possibly discovering a means of hibernation that doesn't involve cooling (lemurs, for example, hibernate in very high temperatures). But regardless, it's encouraging to know that there is a means to reach interstellar space that is considered physically possible, even if it will take a lot longer.